According to a study published in Science, an increase in insured hospital patients due to Medicaid expansion made way toward a 40 percent increase in their visitations to the emergency room (ER).

Moreover, based on a Medicaid lottery program in Oregon, registration in Medicaid increased the probability of ER use by 7 percent, according to lead researcher Sarah Taubman of the National Bureau of Economic Research in Cambridge, Mass.

"These findings speak to one cost of expanding Medicaid, as well as its net effect on the efficiency of care delivered, and may thus be a useful input for informed decision-making balancing the costs and benefits of expanding Medicaid," Taubman and her team wrote.

The researchers divided emergency department visits based on time of day and whether or not they led to an admission. Around 90 percent were defined as outpatient emergency department visits and increased visits from Medicaid enrollees were "solely in outpatient visits."

Expansion of Medicaid connected with an increase in visits in all categories except those considered "emergent, nonpreventable." According to findings of the study, the greatest increase was among visits considered "primary care treatable" and "non-emergent.”

Additioanlly, the researchers noted several factors that limited the generalizability of the study, including the principally white and city-based population used for the study, the fact that signup for the study was voluntary, and the lack of follow-up study on patients' use of emergency services after 13 months.

"These limitations to generalizability notwithstanding, our study is able to make use of a randomized design that is rarely available in the evaluation of social insurance programs to estimate the causal effects of Medicaid on emergency department care. We find that expanding Medicaid coverage increases emergency department use across a broad range of visit types, including visits that may be most readily treatable in other outpatient settings,” the researchers wrote.